Even if it is the kidneys that expel the toxins in the end, they have first been processed by the liver.
I find your symptoms sound more like a liver problem. Try adding digestive enzymes, Betaine HCl and especially bile to every meal. There are supplements that combine the three.
Heavy metals are processed in the liver and bound so that they can be eliminated via the stool. The liver needs bile for this. If your stomach is not acidic enough, bile will not be released (just as the digestive enzymes will not be released either). So adding the bile helps your liver process toxins. Even if your body is not able itself to produce enough of HCl, enzymes and bile, by adding them to your meals, your liver will still be able to detox you.
If you have a digestive problem, then it is still best to figure out why of course. First thing on my list would be a zinc taste test: dissolve a 50 mg zinc picolinate capsule in 250 ml of water and stir well. Some residue will remain, that is the magnesium stearate etc, ignore that. Take a tablespoon full in your mouth and swish. This solution should taste vile immediately. If it doesn't your deficient. Zinc (and Iodine and more) is vital for stomach acidity and other parts of the digestive system.